The present invention relates to a control apparatus and method for an automatic transmission system having a serial arrangement of a continuously variable transmission (or a continuously variable transmission mechanism) and a stepwise variable transmission (or a stepwise variable transmission mechanism), which is capable of performing cooperative shift control in which shift of the continuously variable transmission is controlled in accordance with a change in transmission ratio of the stepwise variable transmission.
Japanese Patent Application First Publication No. 5-079554 discloses an automatic transmission system for a vehicle in which a continuously variable transmission and a stepwise variable transmission are arranged in series. In the conventional art, upon carrying out a shift operation of the stepwise variable transmission, cooperative shift control is conducted, in which shift control of the stepwise variable transmission and shift control of the continuously variable transmission depending on change in transmission ratio of the stepwise variable transmission are simultaneously performed in order to suppress occurrence of change in a total transmission ratio of the stepwise variable transmission and the continuously variable transmission.